Loans Receivable, Net - Additional Information (Detail) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($) loan	Sep. 30, 2023 security_loan	Sep. 30, 2023 loan	Sep. 30, 2023	Dec. 31, 2022 USD ($)	Dec. 31, 2022 security_loan	Dec. 31, 2022 loan	Dec. 31, 2022	Dec. 31, 2021 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average risk rating										2.9				2.9
Increase in CECL reserve	$ 99,548	$ 27,284	$ 10,454	$ 11,407	$ 10,803	$ (2,458)
CECL reserve	463,423	363,875	336,591	144,431	133,024	122,221	$ 463,423				$ 326,137				$ 124,679
Number of loans								185	185			203	203
Net book value	23,252,478						$ 23,252,478				24,691,743
Cash proceeds	10,200
Number of loan modifications | loan							4
Loans held	24,912,876						$ 24,912,876				26,810,281
Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loan modifications | loan							2
Extension term							6 months
Contributions to reserve account							$ 2,000
Interest rate increase							5.11%
Exit fee percentage							4.00%
Aggregate amortized cost basis of loans							$ 286,700
Percentage to aggregate loans receivable portfolio							1.20%
Extended Maturity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loan modifications | loan							2
Aggregate amortized cost basis of loans							$ 435,100
Percentage to aggregate loans receivable portfolio							1.80%
Extended Maturity, Loan One
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extension term							19 months
Contributions to reserve account							$ 4,900
Interest rate reduction							2.74%
Repayment due by borrower at maturity period							$ 2,500
Extended Maturity, Loan Two
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extension term							4 years 6 months
Contributions to reserve account							$ 2,000
Interest rate increase							8.50%
Increase to loan commitment							$ 50,000
Unfunded Loan Commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in CECL reserve	(2,648)	523	(631)	841	2,180	(9)
CECL reserve	13,624	16,272	15,749	9,275	8,434	6,254	13,624				16,380				6,263
Unfunded loan commitments	2,671,851						2,671,851				3,806,153
Unfunded Loan Commitment | Payment Deferral
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded loan commitments	10,000						10,000
Unfunded Loan Commitment | Extended Maturity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded loan commitments	40,000						40,000
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan									74				80
Loans held	6,068,116						6,068,116				6,330,153
Impaired loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in CECL reserve	108,150	17,143	7,480	0	0	0
CECL reserve	322,551	214,401	197,258	54,874	54,874	54,874	322,551				189,778				54,874
Interest income							0
Impaired loans | Unfunded Loan Commitment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase in CECL reserve	0	0	0	0	0	0
CECL reserve	0	$ 0	$ 0	$ 0	$ 0	$ 0	0				0				$ 0
Impaired loans | Three Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans | loan									3
Interest income	7,200
Impaired loans | Ten Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
CECL reserve	322,600						322,600
Number of loans | loan									10
Net book value	1,400,000						1,400,000
Joint Venture | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held	$ 639,200						$ 639,200				$ 795,600